Cellulose is a valuable renewable energy resource. Glucose, fructose and their oligomers which can be obtained by the hydrolysis of cellulose are expected to be valuable chemicals, food and feed stock.
Various methods using acid catalyst or enzyme have been proposed for the hydrolysis of cellulose to recover glucose. It was reported that the low temperature (100-120° C.) concentrated acid hydrolysis of cellulose provided glucose yields approaching 100%. Acid hydrolysis of cellulose in high temperature water produced 71% of theoretical maximum yield of glucose. The process conditions were 215° C., 34.5 MPa and 120 min with 0.05 wt % sulfuric acid.
Supercritical and near supercritical fluids have been described for processing cellulosic materials, e.g. recycling cellulose esters from the waste from cigarette manufacture (U.S. Pat. No. 5,328,934); removing adhesives from cellulose (U.S. Pat. No. 5,009,746); extracting terpenes and oils from wood (U.S. Pat. No. 4,308,200); removing lignin from Kraft streams (U.S. Pat. No. 4,493,797); removal of the natural oils from plant matter (U.S. Pat. No. 4,675,198) and forming cellulose acetate articles (U.S. Pat. No. 5,512,231).
Examples of other related references are: Sasaki et al. “Cellulose hydrolysis in sub-critical and supercritical water” Journal of Supercritical Fluids (1998) 13:261-268; and Adschiri et al. “Noncatalytic Conversion of Cellulose in Supercritical and Sub-critical Water” Journal of Chemical Engineering of Japan (1993) 26(6):676-680. Miyazawa et al. report a 14-fold increase in glucose yield with CO2 addition at sub-critical water conditions (200° C. for 15 min residence time).
Commercial applications of supercritical fluid extraction include the decaffeination of coffee and tea; extraction of hops flavors for beer manufacture; and denicotination of tobacco. Such commercial processes have been used and are described in reviews such as: McHugh and Krukonis, Supercritical Fluid Extraction: Principles and Practice, Butterworths, (1986); Eckert et al., Environmental Science and Technology, Vol. 20, pp. 319-325, (1986); “Supercritical Fluids”, Kirk-Othmer Encyclopedia of Chemical Technology 3rd ed., John Wiley & Sons, New York.
All patents, patent applications, documents, and articles cited herein are herein incorporated by reference in their entirety.